The system of rat cortical neurons grown in dissociated cell culture is being developed as a model with which to study the normal physiological and pharmacological properties of mammalian cortical neurons by techniques which cannot be applied to intact CNS. Putative neurotransmitters (including amino acids, acetylcholine, biogenic amines and neuropeptides) will be applied to the neurons while transmembrane effects are monitored with intracellular recordings. "Postsynaptic" effects of these agents on resting membrane potential, membrane conductance and on the action potential mechanism, and their "presynaptic" effects on axon terminals will be studied. Interactions of each of these agents with both endogenous neurotransmitters and exogenously applied neurotransmitters will also be examined. Abundant excitatory and inhibitory synaptic connections form in culture and we will study: (1) the nature of the transmitters used, (2) the ionic mechanisms underlying the transmitter actions, (3) the regulation of the action of the transmitters, (4) the quantum contents of excitatory and inhibitory synapses, (5) the localization of the synaptic contacts, and (6) the kinds of small circuits which form. Our results have already indicated that GABA is the agent used for all, or almost all, inhibitory transmission in the cultures. The model system will also be used to study pathophysiological mechanisms of epilepsy. The effects of alterations in the extracellular microenvironment (similar to those seen in epileptic cortex) on neuronal physiology and synaptic function will be studied. In addition, the presynaptic elements in pairs of synaptically coupled neurons will be stimulated with patterns which mimic those seen in neurons during epileptic discharges in order to determine how excitatory and inhibitory synapses respond to such stimulus modes. Finally, we will study the effects of three different anticonvulsant drugs on normal membrane physiology and synaptic pharmacology and on pathophysiological epileptic phenomena, in order to determine how these drugs act at the cellular level and how they are able to function as anti-seizure agents.